The present invention relates to a method and a device for sealing, a bearing in which lubricant is used.
As to the method for sealing a bearing in which lubricant is used, a first example of prior art is shown in FIGS. 9 and 10. In this prior art regarding the connection of a rear-axle tie rod and a cylinder arm in a steering unit for a forklift truck, the cylinder arm 71 is held by upper and lower tie rods 72, 73 with a washer 75 of a disc spring interposed between the cylinder arm 71 and each of the tie rods 72, 73, and a tie-rod pin 74 is inserted through the cylinder arm 71, the tie rods 72, 73, and the washers 75 to fasten them. A collar 77 that serves as a bearing member is fitted between the sliding surfaces of the cylinder arm 71 and the tie-rod pin 74, thereby supporting the cylinder arm 71 pivotally around the tie-rod pin 74. The tie-rod pin 74 is provided at the top thereof with a nipple 78 through which lubricating grease is supplied. The surface of the tie-rod pin 74 which slides over the collar 77 is formed with a supply port 74a which is opened to a circumferential groove 74b of the tie-rod pin 74. The supply port 74a is connected to the nipple 78 through a communication passage 74c which is formed axially in the tie-rod pin 74. Grease supplied from the nipple 78 to the sliding surfaces of the collar 77 and the tie-rod pin 74 smoothens the pivotal movement of the cylinder arm 71.
A second example of prior art which is disclosed by Japanese Unexamined Patent Publication No. 10-338156 shows a structure for sealing a gear housing in a steering unit. In this prior art structure, washers are interposed between a dust boot and the inner ends of a pair of right and left tie rods, respectively. A lip made of an elastic material is baked to the inner peripheral edge of each washer in close contact with the outer peripheral surfaces, of bolts thereby to prevent the ingress of water. Therefore, when each washer is interposed between the dust boot and the inner ends of the tie rods to be firmly sandwiched therebetween, the lip is pressed in tight contact. With the flat surface of a bushing inserted in bolt holes of the inner ends of the tie rods and the outer peripheral surfaces of the bolts thereby to prevent the ingress of water from without.
In the above-mentioned first example of prior art, however, the rear-axle tie rod is firmly connected with the cylinder arm by only the washer 75 which is made of a disc spring and disposed between the cylinder arm 71 and the tie rod 72 (73) In this case, although the ingress of foreign matter is prevented, there is fear that liquid such as water may enter into sealing area through the paths C, D as shown in FIG. 10. When water enters into the sealing area, grease in a sliding portion is forced out of the sealing area, resulting in poor lubrication hence development of rust.
Although the lip seal washer which is disclosed by the above-mentioned second example of prior art solves the problem of the first example of prior art by preventing the ingress of water by having the lip which improves the sealing of the gear housing, it Is difficult to discharge or remove old lubricant out of the sealing area. Consequently, the lubricant supply from the nipple 78 of the first example of prior art cannot be performed.